Series-parallel pump



Oct. 25, 1960 R. MlLLER 2,957,426 i SERIES-PARALLEL PUMP A TTOPNEV Oct. 25, 1960 R, C, MlLLER 2,957,426

SERIES-PARALLEL PUMP 4 Sheets-Sheet 2 Filed Dec. 17, 1956 INVENTOR. RALPH C. MILLER BY 'M Y a 06 Arrow/Ey Oct. 25, 1960 R. c. MILLER SERIES-PARALLEL PUMP 4 Sheets-Sheet 5 Filed Dec. 17, 1956 INVENTOIL RALPH C. MILLER ATTORNEY Oct. 25 1960 R. c. MILLER 2,957,426

SERIES-PARALLEL PUMP Filed Dec. 17, 1956 4 Sheets-Sheet 4 @A f/G 9 INVENToR. RALPH C. MILLER A TTOPNEV valve rings of United States PatentO 2,957,426 SERIES-'PARALLEL PUMP Ralph IC. Miller, 540 Eaton Ave., Redwood City, Calif. Filed Dec. 17, 1956, Ser. No. 628,766 Claims. (Cl. 10'3-106) This invention relates to a series-parallel, multiple stage hydraulic pump and to means for operating the same.

Series-parallel hydraulic pumps having several stages which may be arranged all in series, all in parallel, or in various combinations thereof, are old in the art. However, it is advantageous to provide pumps of this character of sectional construction to facilitate the addition or subtraction of sta-ges according to requirements; to provide a means for operating the valving of the stages to adjust the pump readily and speedily to operate in series, in parallel or in various series-parallel combinations; and to employ the pump for various useful purposes such as driving a vehicle.

It is an object of the present invention to provide improvements upon series-parallel hydraulic pumps.

It is a further object of the invention to provide a series-parallel hydraulic pump of sectional construction which facilitates the addition and subtraction of stages.

Yet another object of the invention is to provide an improved valving means for the stages of a series-parallel hydraulic pump.

vA still further object of the invention is to provide valve control means for multiple stage series-parallel pumps of the character described whereby the adjustment of the pump can be carried out speedily and with ease.

Yet another object of the invention is to provide a pump of the character described and means whereby it can be integrated into a system for performing some useful function such as driving a motor vehicle forwardly and in reverse. Y

These and other objects of the invention will be apparent from the ensuing description and the appended claims.

`One form of the invention is illustrated by way of example in the accompanying drawings, in which Figure 1 is a view in longitudinal midsection through the multiple stage centrifugal pump of the invention.

Figure 2 is an end view as seen from the left of Figure 1.

Figure 3 is an end view of one of the control valves (the series-parallel control valve) of the pump of Figure 1, showing in phantom lines the ducting thereof.

Figure 4 is a staggered section taken along the line 4--4 of Figure 3.

Figure 5 is a view in side elevation of another control valve (the distributor valve) employed with the pump of Figure 1, showing in phantom lines some of the interior construction.

Figure 6 is a section Figure 5.

Figure 7 is a fragmentary view taken along the line 7-7 of Figure 1, but on a larger scale, showing the manner in which the valve rings of the pump of Figure 1 are operated.

Figure 8 is a view in front elevation of one of the the pump of Figure 1.

taken along the line 6-6 of Patented oct. 25, 1960 Figure 9 is a view in side elevation of the valve ring of Figure 8 as seen from the right of Figure 8.

Figure 10 is a view in front elevation of one of the castings employed as the main frame member of one of the stages of the multiple stage hydraulic pump of Figure 1.

Figure 11 is a View in end elevation of one of the impellers of the multiple stage pump of Figure 1.

Figure 12 is a diagrammatic view showing a means whereby the pump of Figure 1 may be employed to operate a vehicle.

Referring now to the drawings and more particularly to Figure 1, a multiple stage, series-parallel hydraulic pump is there shown which is constructed in accordance with the invention and is generally designated by the reference numeral 10. It is provided with a main housing 11 having end plates 12 and 13. An impeller shaft 14 is journaled in the end plate 13 and also in the end plate 15 of an impeller housing 16. The latter is xed to the end plate 13 by stay bolts 17. As will be apparent, the pump 10 is 0f sectional construction such that more or less stages may be employed, thereby increasing or decreasing the capacity of the pump. ln the instance shown, six stages are employed. A reservoir 18 is provided which is located between the main housing 11 and the impeller housing 16, such reservoir having an inlet at 19 and an outlet at 20 for the impeller housing. Impellers are provided at 21 which are iixed to the impeller shaft 14. Each impeller 21 has spiral impeller lblades 21a (see Figure ll) and is of the enclosed type having an enclosure member 2lb.

The six stages of the pump 10 are designated by the consecutive numerals 25, 26, 27, 28, 29 and 30. Each stage has inlet openings at 40, 41, 42, 43, 44 and 45, respectively, and outlet openings at 50, 5l, 52, 53, 54 and 55, respectively. The inlet openings 40 to 45 communicate with the reservoir 18 and the outlet openings 50 to 55 communicate through a manifold space 56 (see Figures 1 and 10) with the outlet opening 20.

Referring now to Figures 1 and 10, each of the stages 25 to 30 comprises a casting 57 which serves as the main frame member of the stage. Each casting 57 comprises a plate 58 which has a central opening and a hub 58a to receive the impeller shaft 14. Ribs 58h are provided for reinforcement purposes. Each casting 57 also comprises an annular rim or flange 59 in which are formed the inlet openings 41 (or 42, 43, 44 or 45) and the outlet openings 50 (or 51, 52, 53 or 54). Interstage ports -60 are formed in the plate 58; also slots 65 which are diametrically opposite one another.

Referring now more particularly to Figures 8 and 9,

` one of the interstage valve rings is there shown and is generally designated as 70a. By referring to Figure 1, it will be seen that a pair of such rings, indicated at 70a and 7017, are provided for Veach of the castings 57. Each ring 70a is intended to open and close the corresponding outlet ports 50, 51, 52, 53 or 54 and each'ring 70h is intended to open and close the corresponding inlet ports 41, 42, 43, 44 or `45. Each ring 70a has a vertical portion 71 formed with interstage ports 72. Pins 75 project from the vertical portion 71 and are received in slots 65 of the corresponding casting 57. Each ring 70a also has a flange 76 which is formed about its top portion with outlet ports 77a. A fork member 78 is fixed to and projects from the ring member 70a for a purpose explained hereinafter.

Each of the valve rings 70b is similarly formed except that its ports 77b are located at the bottom to register with the inlet ports 41 (or 42, 43, 44 or 45).

Consider now, the second stage 26. lts outlet valve ring 70a works with the inlet valve ring 701; of the third stage 27, and its inlet valve ring 70b works with the outlet valve ring 70a of the lirst stage 25. Thus, the pins 75 of the ring 70b of the second stage 26 and the pins 75 of the ring 70a of the first stage 25 are located in the slots 65 of the first casting 56. Accordingly, these rings must move in unison. When this pair of rings 70a and 7Gb is moved to one extreme position (which is determined by the respective Vslots 65, and which may be called the series position) the following conditions prevail: The interstage ports 72 of the rings 70a and 7Gb are in registry with the interstage ports 60 of the lirst casting 57; therefore, liquid will ilow from the lirst stage 25 into the second stage 26. Therefore, these two stages are connected in series. Moreover, the outlet ports 77a of the ring 70a are out of registry with the outlet ports 50 in the impeller housing 16; and the inlet ports '77'b of the ring '7011 are out of registry with the inlet ports 41 of the impeller housing 16.

If the rings 70a and 7017 areA rotated to their other extreme position (which. is also determined by the slots 65, and which may be called the parallel position) the interstage ports 72 of the rings 76a and, '701) will be out of registry with the interstage ponts 60' of the casting 57. Therefore, the stages 25 and 26 are not interconnected. Moreover, the outlet ports 77a of the ring 76a will be in registry with the outlet ports fili, and the inlct ports 771') will be in registry with the inlet ports 4'1. Therefore, the stages 2S and 26 will be in parallel.

Similarly, each of the castings 57 has a pair of valve rings 70a and 70b which operate together and determine whether the two associated pump stages are connected in series or are in parallel.

lf all of the ve pairs of valve rings 70a, 7Gb are rotated to their series positions, then all of the stages will be in series and the pump will operate as a six stage series pump with liquid entering through the ports 40 (one of which is shown at fthe lower left in Figure l and which are always open) and will leave through the ports 55 (one of which is shown at the upper right in Figure l and which are always open), thence out through the manifold chamber 56 and outlet 20. A minimum volume of liquid will, therefore, be pumped at a maximuni pressure.

If, on the other hand, all of the live pairs of valve rings 70a, 70h are rotated to their parallel positions the pump will operate asa six stage parallel pump with liquid entering the six stages through the ports 40, 41, 42, 43, i4 and 45 and leaving throughk the ports 50, 5 1, 52, 53, 54 and 55, thence out through the manifold space 56 and outlet 20. The pump will, therefore, pump amaximum volume of'liquid at minimum pressure.

If the pair of valve rings 70a, 706 which are associated with the third casting 57 are placed in their parallel position and the other pairs of rings are placed in their series positions, thel pump will operate as, two three stage series pumps operating in parallel; i.e., liquid will enter the first three stage pump at 40 and will leave at 52 and liquid will enter the second threev stage pump at 43 and will leave at 55.

lf the pairs of valve rings 70a, 'tb associated with the second and fourth castings 57 are placed in their parallel positions and theother Valve rings are placed in their series positions the pump will function as three two stage pumps operating in parallel. Liquid will enter through the ports 40, #i2 andV 44 and will leave through the ports 51, 53 and 55.

It will, therefore, be apparent that a series-,parallel hydraulic pump has been provided in which allof the stages may be operated in series, in paralleler in, various series-parallel combinations to provide in one case (series operation) a minimum volume output atv maximum pressure, in another case (parallel operation)v a maximum Volume output at minimum pressure and, in intermediate cases (series-parallel combinations) with intermediate volumes and pressures.

Referring now to Figures l and 7, one of the stay bolts 17, which is shown at the bottom of Figure 1 serves also as a shaft to support three concentric sleeve: 85, 86 and 87. The innermost sleeve 85 is rotatable or the stay bolt 17; the intermediate sleeve 86 is rotatable on the sleeve and the outermost sleeve 87 is rotatable on the intermediate sleeve 86. The innermost sleeve 8E is the longest of the three sleeves. At its right-hand end (as viewed in Figure l), the sleeve 85 is connected by a lever 88 and pin 88a to the fork 78 of the valve ring 70a associated with the fifth casting 57. The lever 88 is connected by a rod 89 to a double acting piston 90 which is reciprocable within a cylinder 91, It will be apparent that, by introducing fluid under pressure into one end of a cylinder 91 and exhausting fluid from the other end of the cylinder, the corresponding pair of valve rings 70a, 70b will be rotated to their series position, and by operating the cylinder 91 in the reverse direction the same pair of valve rings 70a, 70b will be rotated to their parallel position.

As illustrated in Figure l, the sleeve 85 extends to the valve rings 70a, 7Gb at the opposite end of the pump and is connected thereto in similar manner. Therefore, two pairs of valve rings 70a, '70h (those associated with the rst and fifth castings 57) are operated in unison. Similarly the sleeve 86 extends between the second and fourth pairs of valve rings 70a, 70b and is connected thereto to operate the same in unison. A cylinder 92 is provided in like manner to rotate these valve rings. The sleeve 87 is associated with only the third pair of valve rings 70a, 70b, which are associated with the third casting 57, and these rings are operated by a third cylinder 93.

It will, therefore, be apparent that the three cylinders 91, 92 and 93 can be used to place the six stages 25, 26, 2.7, 28, 29 and 30 all in series, all in parallel, or in either of the two series-parallel combinations, i.e., two three stage pumps operating in parallel or three two stage pumps operating in paralle Each of the cylinders 91, 92 and 93 may be regarded as having a series end and a parallel end. That is, if fluid under pressure is delivered to the series end of a cylinder, it will operate that cylinder to move the corresponding valve rings 70a, 70b to their series position, and if Huid is delivered under pressure to the parallel end of a cylinder it will move the corresponding valve rings 70a, 70b to their parallel position.

Referring now to Figures 3 and 4, a control valve is there shown which is generally designated as 10i)` and which is intended to operate the hydraulic cylinders 91, 92 and 93 to accomplish the permissible operations described hereinabove. That is, it is the function of the valve to control the delivery of pressure tothe cylinders 91, 92 and 93 so that the pump 10 can be operated in four different ways, to wit, as a six stage series pump, as apump. operating with six stages in parallel, and in the two series-parallel combinations described above, i'.e., two three stage pumps operating in parallel and three two stage pumps operating in parallel.

The valve 100 has a valve body 101 n which a rotor shaft 102 is j'ournaled and to the inner end of which (at the left as viewed in Figure 4) is-xed a rotor 103.

pressure from a suitable source of pressure such as an hydraulic pumpI (notl shown). The valve body 101 is formed with aY fluid outlet at 106 which connects to a suitable reservoir (not shown).

The valve body 101 is also formed with six ports which are arranged in pairs. The ports 1118, 112S and 1-13S series ends of the cylinders 91, 92 and whereas the ports 1'11P, 112P and 113P are connected by suitable ducts (not shown) with the parallel ends of the cylinders 91, 92 and 93, respectively.

The rotor 103 is formed with nine pressure ports which are indicated by the reference numerals 1p, 2p3p, 4p, 5p,

93,- respectively,

6p, 7p, Sp and 9p, and it is also formed with nine exhaust ports which are designated as 1e, 2e, 3e, 4e, 5e, 6e, 7e, 8e and 9e. Two such ports (the pressure port 4p and the exhaust port 2e) are shown in the staggered section of Figure 4. It will be seen that the pressure port 4p is adapted to register with a series port (e.g., the port 113S) in the valve body but that it cannot register with a parallel port in the valve body. I-t will also be seen that the exhaust port 2e is adapted to register with a parallel port (e.g., the port 113P) but that it cannot register with a series port. Similarly each of the pressure ports 1p, 2p, 3p, etc. is adapted to register only with -a series port 111S, 1128 or 113S and each of the exhaust ports 1e, 2e, 3e etc. is adapted to register only with a parallel port 111P, 112P or 1131. Also each of the pressure ports 1p, 2p, etc. connects with the pressure inlet 105 of the valve 100 and each `of the exhaust ports 1e, 2e, etc. connects with the pressure outlet 106 of the valve 100.

It is intended that the rotor 103 be rotated in twenty degree increments between the position shown in Figures 3 and 4 (which will be referred toas position A) and a position sixty degreesfrom that shown in a clockwise direction (such position being referred to las position D). There will be two stops between position A and position D, i.e., a position twenty degrees and another position forty degrees fromposition A; such intermediate stops or positions being referred to as position B, and position C, respectively.

In position A, it will be seen that pressure ports 1p, 4p and 7p connect the series ports 111S, 113S and 112S, respectively, and that exhaust ports 9e, 5e and 2e connect with parallel ports 1111 112 P and 113P, respectively. Therefore each of the cylinders 91, 92 and 93 is connected to pressure at its series end, hence allrofpthe valve rings 70a and 70b will be placed and held in their series positions. Therefore, the pump 10l will operate as a sixlstage series pump. f

Assume now that the rotor 103 is turned 20 in clockassi-rae wise direction to position B. ltshould be noted that suitable spring-actuated detent means (not shown) may be employed to hold therotor in each of its four positions and that suitable stops (not shown) may be employed to prevent the rotor from passing beyond position A in one direction or position Bin the other direction. Y

When the rotor 103 is imposition B the ports will align as follows: Pressure port V9p will register with series port 111S andrexhaust port 8e will register with parallel port 1111. Therefore, cylinder 91 will remain undisturbed.

Pressure port 2p will register with parallel port 1131 'and exhaust port 3e will register with series port 11384.

Therefore, cylinder 93 .will be reversed and will be in its parallel position.

Exhaust port 4e will' register with parallel port 112P and pressure Vport 6p will register with series port 112S. Therefore, cylinder 92 will remain undisturbed.

With cylinders 91 'and 92 in series position and cylinder 93 in parallel position it follows that stages 25, 26 and 2.7 will be in series with one another; that stages 27 and 28 will be parallel to one another; and that stages 28, 29 and 30 will bein series with one another. Therefore, the pump in position YB will operate as two three stage pumps in parallel with one another. Y

Assume now Vhat the rotor is turned another 20 clockwise to positionV C. The alignment of the ports will -be asfollows: i*

Exhaust port 7e will register with parallel port 111P and pressure port 8p will register with series port 111S. Therefore cylinder91 will be in series position.

, Exhaust port 1e will register` with parallel port 113P and pressure port 3p will register with series port 113S. Therefore, cylinder 93 will be in series position.

Pressure port 5p will register with parallel port 1121 and exhaust port 6e will register with series port 112S. Therefore, cylinder 92 will be in parallel position.

With cylinder 91 in series position, cylinder 92 in paralverse ports; and it is also formed lel position and cylinder 93 in series position the first and second stages 25 and 26 will be in series with one another; the third and fourth stages 27 and 28 will be in series with one another; and the fifth and sixth stages 29 l'and 30 will be in series with one another. Each of these pairs of stages (i.e., 25, 26', 27, 28; 29, 30) will be parallel tothe other pairs. Therefore, the pump in position C will operate as three two stage pumps operating parallel to one another. Y

Finally, assume that the rotor is turned another 20 clockwise to'position D. In this position the ports align as follows:

' Pressure `port 7p will register with parallel port 111P 'andA exhaust port 9e will register with series port 111S. jy VPressure port 1p will register with parallel port 1131 and exhaust port 2e will register with series port 113S.

" Pressure port 4p will register with parallel port 112P `and'exha'ust port 5e Aw'll register with series port 112S. It will, therefore, b e apparent that in position D, the parallel e'rid of each of the cylinders 91, 92 and 93 is connected with pressure. Therefore, all of these cylinders will Vbe in their parallel position; hence all of the valve rings 70a and 70b will be in their parallel positions. Therefore, the pump 10 will operate at six single stage pumps operating lin parallel to one another.

` It will, therefore, be apparent that the control valve 1'00 is effective to operate the pump 10 in the intended manner asja six stage series pump; as a parallel pump consisting of six single stage pumps operating in parallel; and in the intermediate 2-3 and 3-2 series-parallel combinations. f AlIt will also be apparent that, in addition to the detent means yand stop means referred to above, a pointer (not shown) may be attached to the rotor shaft 102 and an in dex may be attached to the valve body 101 so that all anloperator need do is rotate the shaft 102 until the pointer pointsV to the desired position on the index.

One of the purposes of the pump 10 is to operate a vehicle such as a truck or bus by supplying hydraulic uid under pressure to hydraulic motors at the wheels of the vehicle. It will be apparent that the pump 10 is well adapted for this purpose. Thus, it can be operated in position A (six-stage, series) to give maximum power at low .speed (i.e., a small volume rate of iiow), thereby providing ya lowest gear ratio between the prime mover andthe traction wheels. Itv may also be operated in position D (six single stages in parallel), hence at lowest pressure and maximum volume rate of flow to provide a highest gear ratio; and at positions B and C to provide intermediate gear ratios. In the meantime the prime mover, which may be a gasoline, diesel engine or any other suitable type of prime mover, may be operated at constantspeed and under conditions of maximum efficiency.

In employing the pump 10 in this manner it is desirable toprovide a control valve capable of delivering fluid under pressure from the pump 10i to the motor of each traction wheel in a forward direction to turn such wheel forwardly; or in a reverse direction to turn each wheel' rearwardly; and also to by-pass the hydraulic :motors ofthe'wheels altogether for idling, e.g., when it is desired to arrest progress of the vehicle without shutting 0E Vthe prime mover and terminating operation of the pump 10. For this purpose there is provided a valve which is illustrated in Figures 5 and 6 and is generally designated by the reference numeral 115.

. V The valve comprises a valve body 116 in which .is rotatable a rotor 117 having a shaft 118. The valve body 116 is formed at one end with a fluid inlet 119.

Thevalve rotor 117 is formed with a diametral passageway 120 which connects with the inlet 119. The

`valve body 116 is; formed with ports 121a and 121b which will be called the forward ports; it is also formed with ports 122a and 12211 which will be called the rewith ports 123a and 123b which will-be called return ports- It will'be seen that each pair oflports, e.g., the ports 121e and 121b, are diametrically opposite one another, and that the six ports are spaced' 60 apart.

Referring now to Figure 12, the hydraulic pumpor motor 10 is there shown together with the controlfvalves 100 and 115', in connection with a vehicle which is shown schematically and is generally designatedv by the reference numeral 130. The vehicle 130 has four traction wheels, the front wheels being designated by the reference numeral 131 and being connected by a front axle 132,y the rear Wheels being designated as 133 and being connected by a rear axle 134. Each of the wheels 131 and 133 is providedwith an hydraulic motor which is generally designated by the reference numeral 135. Any suitable type of hydraulic motor may be employed, preferably of positive displacement type, for example, gear pumps. As is well known, a device of this character having a positive displacement will operate at a speed corresponding to the throughput of liquid, that is, the volume rate of flow of liquid.

The connections of the control valve 1115 will be apparent from an inspection of Figure 12. Thus, the forward ports 12111 and 1'21b are connected by lines '12111 and 12111 to the hydraulic motors 135, the connections being such that each of these motors will be driven in the forward direction if fluid is delivered through these lines. Fluid discharged from the motors'135 will vreturn through the lines 122g and 1221) to the control valve115, whence it will return through the ports 123a and 123b (see Figure 6) and similarly numbered lines shown in Figure l2, to the reservoir 18 (see Figure 1). Accordingly, the vehicle will be driven in the forward direction.

If it is desired to drive the vehicle in the reverse direction the valve rotor 1-17 will be turned 60 to the right, i.e., in counterclockwise direction as viewed in Figure 6 to bring the diametral passageway 120 o`f the valve rotor 117 into registry with the reverse ports 122a and Ll22b. It will he apparent that hydraulic fluid will be forced through the motors 135 in the reverse direction, returning through the lines 121a and 121b. Hence the vehicle will be driven in reverse.

If it is desired to disengage the pump 10 from the wheels of the vehicle, this is accomplished by rotating the valve rotor 117, 60 to the left from the position shown in Figure 6, thereby bringing the diametral passage 120 of valve rotor 117 into registry with the return ports 123a and 123i). It follows that fluid entering the valve through the inlet 119 (see Figure 5) will be recycled to the reservoir. Accordingly, no fluid will be delivered to the hydraulic motors 135, the wheels 131 will not be driven and the pump l will idle.

It will be further apparent from the description above and from the drawings that in driving the vehicle'in either the forward or reverse direction, the power supply can be delivered at a low gear ratio (with the valve 100 :in position A and the six stages of the pump operating in series); or in high gear (with the control valve 100 in position D and the six stages operating in parallel); or in either of two intermediate gears. A control lever 140 (see Figure 2) and a scale or index (not shown) may be -employed to operate the valve 115.

It will, has been therefore, be apparent that an hydraulic pump provided having certain advantageous features among which are a sectional or segmental construction allowing the addition or subtraction of units to suit particular requirements; and a high degree of fiexibility, being capable of operating at very high, very low and intermediate gear ratios. It will further be apparent that vnovel and very useful control valves have been provided for the operation of the pump. Among the advantages of operating a vehicle by the system described may be mentioned the following: A prime rnover rnay be employed such. as. av gasoline-motor or a diesel engine which is allowed: to operate at constant speed, the speed being se- Iected for maximum efficiency of operation. The vehicle can be operated forwardly and in reverse at any gear ratio desired and can be caused to idle.

I claim:

l.. A multiple stage series-parallel rotary pump comprising a shaft, a plurality of rotors fixed thereto and each adaptedl to limpart an increment of pressure to a liquid; enclosure means for each rotor formed with series inlet and outlet ports and parallel inlet' and outlet ports to operate such rotor in series and in parallel, respectively, in relation to fore and aft stages; and means for selectively opening and closing such ports comprising ro- Atatable valve rings associated with each impeller to open the series ports and close the parallel ports when in a tirst position and to reverse such ports when in a second position; said selective means also comprising a plurality of concentric rotatable sleeves, means connecting each sleeve with at least one set of valve rings and iiuid pressure operated, double-acting cylinder means for rotating said sleeves.

2. Series-parallel apparatus of the character described comprising: A rotatable shaft; a plurality of impellers fixed to said shaft in tandem; a partition between each adjacent pair of impellers; and a housing enclosing said impellers; Said impellers being N in number and being designated in succession as the first through the Nth irnpeller, N being an even number not less than 4; said housing having an inlet for the first impeller, an outlet for the Nth impeller, outlet apertures for the first through the V(N--1)th impellers and inlet apertures for the second through the Nth impellers; each said partition having an opening for connecting its respective pair of impellers in series; each said partition having also a first face nearer the first impeller and a second face more remote from the first impeller; said apparatus also comprising a first set of valve plates rotatable on the first faces of the said partitions and a second set of valve plates rotatable on the second faces of said partitions; each such first valve plate also having an outlet aperture for registration with the adjacent outlet aperture of the housing; each such second valve plate having an inlet aperture for registration with the adjacent inlet aperture of the housing; each pair of valve plates associated with a partition having a pair of openings for registration with the opening of such partition, each pair of valve plates being interconnected in such a manner that they rotate in unison between a first position connecting the respective pair of impellers in series and a second position connecting such pair of impellers in parallel.

3. The apparatus of claim 2 including liuid pressure operated means for operating said valve plates.

4. The apparatus of claim 2 including a plurality of concentric shafts and means connecting said shafts to said valve plates to operate the latter by selective rotation of the shafts.

5. The apparatus of claim 4 including also a master control valve for selective rotation of said shafts.

References Cited in the file of this patent UNITED STATES PATENTS '1,099,161 Brown June 9, 1914 1,231,310 Taylor June 26, 1917 1,242,033 Painter Oct. 2, 1917 1,374,747 Kuroishi Apr. l2, 1921 2,044,830 Carlstedt June 23, 1936 2,583,242 Turkenkoph Jan. 22, 1952 2,688,981 Greer Sept. 14, 1954 FOREIGN PATENTS v11,558 Great Britain of 1909 

